1. Field of the Invention
The present invention relates to a fiber-optic sensor for measuring or sensing changes in a physical quantity such as pressure, force, acceleration, flow or level and makes of interference patterns generated by multiple reflections between parallel surfaces. A sensor according to the invention would be used in measuring euqipment which includes a transmitter and a receiver unit, respectively arranged to transmit to and receive from the sensor, optical energy. A sensor according to the invention may also include at least one optical fiber for the transmission of optical energy to and from the sensor which has to be located at the point at which the physical quantity is to be measured or sensed.
2. Description of the Prior Art
In the specification of co-pending U.S. patent application Ser. No. 708,095 (the entire disclosure of which is herein incorporated by reference) filed on Mar. 4, 1985 by Brogardh and Ovren (and assigned to the common assignee of this application ) as a Continuation of application Ser. No. 218,949 there is disclosed a fiberoptic measuring device for measuring a physical quantity such as pressure, force, acceleration, flow, level, temperature or the like which device employs a photo-luminescent body, the geometrical position of which, in relation to an optical fiber, constitutes a measure of the physical quantity to be measured. The position information, such as intensity modulation of one or more wavelength intervals of photoluminescent optical energy, is made available to a transmitter/receiver unit. Since the position information is related to the dimension of the optical fiber, the available range of measurement, and thus the resolution of the device, are limited.
the utilization of modern semiconductor manufacturing processes is a natural choice for the above-mentioned sensors. Their manufacture can then take place in large batches, so that the cost of manufacturing each sensor unit will be largely proportional to the square of the dimensions of the sensor. There if therefore a strong incentive to obtain as high a degree of miniaturization as possible. For sensors which rely upon a measurement of position, the degree of miniaturization of the available measuring range is restricted by non-linearities and physical aspects. Thus, to make the fullest use of available miniaturization techniques, it is desirable to produce a sensor which relies naturally on small size and which can, therefore, provide high accuracy of meaurement even for a very small sensor.
For acoustic applications and cases where a vibration measurement is to be made, there exist further reasons for searching for a miniaturized sensor design which will provide high-resolution accuracy.